1. Field of the Invention
The present invention relates to an internal combustion engine of the split type having a plurality of cylinders split into first and second groups, the first group of cylinders being always active and the second group of cylinders being inactive when the engine load is below a given value.
2. Description of the Prior Art
It is generally known that internal combustion engines demonstrate better fuel combustion and thus higher fuel economy when running under higher load conditions. In view of this, split type internal combustion engines have already been proposed as automotive vehicle engines or the like which are subject to frequent engine load variations. Such split type internal combustion engines include a group of cylinders which are always active and a group of cylinders which are inactive when the engine load is below a given value. The intake passage is divided into first and second branches, the first branch being associated with the active cylinders and the second branch being associated with the inactive cylinders. A stop valve is provided in the second branch and adapted, in its closed position, to cut off the flow of air to the inactive cylinders so that the engine operates only on the active cylinders at low load conditions. This increases the load on the active cylinders resulting in higher fuel economy.
An exhaust gas recirculation system has been incorporated in such a split engine for re-introduction of a significant amount of exhaust gases into the inactive cylinders in order to minimize inactive cylinder pumping losses during a split engine operation. It has been found, however, that exhaust gases escape through the stop valve from the first intake passage branch into the second intake passage branch, resulting in unstable active cylinder operation during split engine operation, especially where a pressure differential exists across the stop valve. Attempts have been made to eliminate the possibility of exhaust gas leakage, but, prior to the present invention, such attempts have been found to be insufficient.